Illustrated in FIG. 1 is a conventional, state of the art supersonic abrasive blasting system 10 comprising a compressor 12, compressor hose 14, and abrasive tank 16 containing abrasive media 18. An abrasive metering valve 20 controls the rate of release of abrasive media 18 into a standard blast hose 22. Release media 18 travels through a blast hose 22 to a claw coupling 24 and through supersonic convergent-divergent nozzle 26 where it is released into the environment at supersonic speed and with considerable noise.
Details of state of the art convergent-divergent nozzle 26 are depicted in FIG. 2 in cross section. Nozzle 26 is comprised of a barrel 28 having a bore 30 with a convergent bore section 32, throat 34, and divergent bore section 36. Carrying gases mixed with abrasive media 18 are compressed when traveling through convergent section 32 and then dispersed through divergent section 36, causing media 18 particles to accelerate within the divergent section 36 of nozzle 26 and out therefrom.
Conventional abrasive blasting system setups utilize a single 1″ inner diameter blast hose 22 with a convergent-divergent type supersonic nozzle attachment 26. The abrasive blasting media in these setups undergo most of their acceleration over a short distance in and following exit from nozzle 26.
As demonstrated in Settles' paper (Settles G., A scientific view of the productivity of abrasive blasting nozzles, 1996), particles accelerate from fairly modest velocities before the nozzle, to higher velocities as the particles flow through the diverging portion of the nozzle and the exit. This minimizes wear in the hose, especially for highly abrasive media. This behavior is illustrated in the graphs reproduced from Settles' paper in FIG. 3, showing predicted and measured velocities through a Laval nozzle.
Currently available abrasive blasting systems as the one depicted in FIGS. 1 and 2 produce excessive noise which exceeds levels set by occupational safety organizations for work environment noise and, as a result, require the use of personal protective equipment for hearing protection as well as time limits for operator exposure to this noise. Accordingly, there is a need for abrasive blasting systems that produce less noise while still demonstrating equivalent productivity and efficiency.
Currently available abrasive blasting systems as the one depicted in FIGS. 1 and 2 are large and heavy, creating stress and fatigue for the user. As such, there is a need for abrasive blasting systems that are smaller and lighter for ease of use and longer periods of use.